The shifted baseline: Prehistoric defaunation in the tropics and its consequences for biodiversity conservation

The majority of terrestrial ecosystems outside Africa have lost megafaunal vertebrates (>44 kg) since the Middle Pleistocene and most of these extinctions can be attributed to human influence. This review assesses the likely impacts of prehistoric megafaunal extinctions in the lowland tropics and discusses the implications for contemporary conservation management. The most likely impacts include: the coextinction of parasites, a reduction in environmental heterogeneity, the release of competitors and prey (including plants), and a loss of quality and quantity in seed dispersal services. This, however, is based largely on arguments by analogy with the surviving megafauna, since the impacts of megafaunal losses are compounded in the paleoenvironmental record with changes in climate and other human impacts. Suggested conservation responses include: prioritizing the conservation of the surviving megafaunal species and reintroducing them, where possible, into parts of their former ranges; reversible experiments with the introduction of taxon substitutes outside their natural ranges; and special conservation attention to megafaunal-dependent orphans and anachronisms.